Rheostat.



PATENTED NOV. l, 1904. W. BAXTER, JR.

RHEOSTAT.

APPLICATION FILED MAR. 5, 190s.

No MODEL. v

1 Bl. .r2 ...vynil 4 Figl.

' this kind to which it belongs.

Unirse STATESv Patented November 1, 1904.

PATENT Qrricn.

WILLIAM BAXTER, JR., OE JERSEY CITY, NEW JERSEY.

SIDECIFICATION forming part of Letters Patent No. 773,777', dated November 1, 1904.

Application filed March 5, 1903. Serial No. 146,366. (No model.)

To all whomjz't may concern: i

Be it known that I, WILLIAM BAXTER, .I r., a citizen of the United States, residingat J ersey City, inthe county of Hudson, State of New Jersey, have invented certain new and useful Improvementsl in Rheostats, of which the following is a specification. A

This invention relates to an improved form of electrical resistance or rheostat, and has for its object increasing the mechanical strength and the durabilityT of the type of apparatus of The resistance consists of one or a number of rods made of material of low conductivity provided with .metallic terminals, by means of which they can be connected with each other and with the circuit in which the device is to be used. Resistance-rods of this kind have been made for several years and in various forms; but they have never been wholly satisfactory even under the most favorable conditions, while when subjected to the severe strain of strong currents they have invariably failed; The material most commonly used for making these rods is carbon in its various forms, such as graphite, lampblack, retort-carbon, &c. If arod of low resistance is required, it is made of pure carbon, generally in the form of graphite. If a higher resistance is desired, a non-conducting materialsuch as clay, talc, &c.-is mixed with the graphite, the proportions of each ingredient being snflicient to give the proper resistance. In some cases where very high resistances are required they are made by mixingI carbon with a metallic oxid, or the oxid alone may be used. are constructed in substantially the same way as is employed in the manufacture of carbon rods for arc-lightsthat is, the material in a pulverized form is mixed with a binder, is then compressed in molds, and finally baked in an oven. The resistance-rods of this kind that have been made have two serious objections, one of which is that they'are easily broken and the other is that the contact with the metallic Atips with which they are provided soon become so imperfect as to render the rod useless.

My invention has for its object making the rods strong, so that they cannot be broken or The rods otherwise injured by the hardest treatment to which they may be subjected and making -the contact with the metallic tips so that it will remain as perfect during the whole life of the resistance as it is when first made. The first of these objects is accomplished by placing the rod within a strong casing made of a non-conducting material, so as to shield it from external injury. The second of these objects is attained by arranging the metallic tips so that they are forced against the resistance by a sufcient pressure to insure a perfect electrical contact, and this pressure Vis maintained as long as the apparatus lasts and is not affected in any way by any condition of usage.

By the aid of Figures l, 2, and 3 the construction of the rheostat in the form which I consider vthe most desirable can be readily understood. As will be shown hereinafter, these drawings only show one of the many forms in which my invention can be utilized.

Fig. lis a front view of a complete rheostat having the resistance-rods connected inf series. Eig. 2 is an end view of the apparatus or a side View of Fig. l. Fig. 3 is a view of Fig. 1 as seen from above.

The six pipes marked l contain the resistance-rods and are held in their proper position by means of the end frames 2 and 3 and the clamping-bolts 4 4. Fig. 2 shows at its upper end a section through the center of the right-side pipe 1 and the resistance-rod it incloses. It also shows a section through the top frame 2. The resistance-rod 5 is incased by a tube made of non-conducting material, (marked 6,) and this latter is incased by the tube I, which is simply a piece of iron gaspipe. The rod 5 can be formed in the usual way, being of such a diameter that it will slide freely into the casing 6, and the latter may also be made separately and of such external diameter that it will slide freely into pipe l. The construction which I prefer, however, is to apply 6 as a lining to l and to force it out tightly against the inner surface of the iron pipe l. The material of which the resistancerod 5 is made is then placed inside of 6 and is IOO pressed any more by any pressure that it may be subjected to when in service. At each end of the rod 5 a metallic plug' 7 is placed, this plug beingsmall enough to slide freely within tube 6. In Fig. 1 two of these plugs 7 are shown in broken lines; but it will be understood that these plugs are provided at each end of all the resistance-rods. To connect the rods 5 in series, the plugs 7 of adjoining rods are connected together by a connector 8, and these connectors are insulated from the frames 2 and 3 by means of the insulation 9. As is shown in Fig. 1, a spring 10, which is held in position by a pin 11, bears against a plate 12, which is directly over the connector 8. With this construction it will be seen that when the bolts 4 4 are tightened up the pressure is transmitted to the plugs 7 through the spring 10. Hence the elastic force of the spring will continually press the plugs 7 against the ends of the resistance-rods 5, and thus maintain a perfect electrical contact at all times.

Fig. 1 shows one spring 10, acting to press plugs 7 against the upper ends of the two rightside resistance-rods. Similarsprings are provided for all'the resistaneerods. If it is desired to reduce the cost of construction, springs can be provided at the upper end only, in which case the insulation 9 at the bottom would rest directly against the frame 3; but unless the casting 3 is made with unusually smooth seat for 9 to rest against it will be advisable to place springs 10 at both ends.

In order that the electrical contact between the plugs 7 and the ends of the rods 5 vmay be perfect, it is necessary that a sufiicient amount of pressure be applied. Therefore the bolts 4 4 must be of such size as to be capable of developing this pressure. In order that this pressure may continue as long as the rheostat lasts, it is evident that the springs l0 must be of such dimensions that they can transmit all the pressure required without being strained beyond their elastic limit or, in other words, without being completely flattened out. The plates 12 should be made so as to not shift out of place endwise while the rheostat is being put together. This can be accomplished by fastening' one end of spring 10 to the corresponding end of 12 or by providing dowelpins or some similar device.

As can be readily seen, the flat spring 10 here shown can be replaced by a spring of any other form that will transmit the pressure of the bolts to the plugs 7. Thus a spiral spring could be placed in a recess central with pin l1, or two such springs could be used in place of one flat spring', so as to have spiral springs directly in line with the resistancerods 5.

Thile the resistance-rods 5 are shown connected in series in Fig. 1, it can be easily seen that they may be connected in parallel or a part of them in parallel and the others in series. The connectors 8 are shown with an extension projecting sidewise 'from the ccnter and terminating in an eye, so as to provide an easy means for making connections with the circuit in which the device is used.

If the resistance-rods 5 are made of very high resistance and are traversed by strong currents, the heat generated may be sufficient to impair the Contact with the plugs 7 by causing the surface of these to become corroded. To obviate this difficulty, the conductivity of the rod 5 is increased at the end by the addition of an excess of the conducting material used in making the rod. In this way the heat generated in the portion of 5 in actual contact with 7 is greatly reduced, and the rising temperature of the joint is d ue mainly to the heat that is conducted to it though the end of 5. To illustrate this construction in Fig. 2, the upper end 5 of the resistance 5 is shown darker than the portion below it.

If the rheostat is to be used with currents of such strength that the temperature will not rise more than a few degrees, any kind of insulating material can be used for the tube 6 as well as for 9, providing its insulating qualities are such that it can withstand the electromotive force to which it is to be subjected. In most cases, however, all the insulation will have to be made of fireproof material, such as mica, asbestos, glass, &c.

.In looking at Fig. 2 it can be seen that the only oiiice of the pipe 1 is to protect rod 5 from external injury. .It is evident that if 1 were removed, the tube 6 would be but a slight protection to 5. There is no difliculty, however, in making' 6 of proper size to provide ample protection for 5, and with such construction 1 would not be required. In the construction of Fig. 2, 6 would be made of mica, asbestos, glass, or some similar material; but 6 can be made in the vforni of a strong tube of porcelain, with walls, say, threequarters of an inch thick, and then it would be strong enough to protect 5 tlioroughly.

In looking at Fig. 1 it can be seen that the pipes 1 can be replaced by a casting having parallel holes through it to receive the tubes 6 and rods 5, and it can also be seen that if 1 is discarded a porcelain block can be made having as many parallel holes as there are resistance-rods 5.

Ihile in Fig. 3 thetrods 5 are shown arranged in a single straight line, it is evident that they may be located in two or more rows, or they may he arranged in a circular line. To vary the location of the resistance-rods in any way desired, all that is necessary is to change the form of the end frames 2 and 3 so that they may be able to properly clamp the springs 10, and thus force down the plugs 7, and to provide as many bolts 4 4 as may be necessary to impart the proper pressure to all the tubes.

lhile it is possible to discard the metallic IOO tubes 1 by substituting for the thin insulatof such material perforated with a number of holes to receive the resistance-rods 5, I prefer the construction shown in the drawings, because it is more compact and, in addition, increases the capacity of the rheostat from the fact that the heat generated in the rods 5 will be dissipated more rapidly than it would be from the porcelain tubes o'r block. Hence the energy-absorbing capacity of a given size rheostat when heated to a given temperature will be greater with the construction shown in the drawings than it would be with porcelain tubes.

Ihile I have shown the plugs 7 forcedl against the ends of the resistance-rods 5, it is evident that the construction can be varied so as to have the. end contacts bearing against the sides or the sides and 'ends of 5 withoutl departing fromjthe general principle of construction of my invention, providing in any such modification the pressure with which the contact is forced against. the surface of 5 is transmitted through a spring of proper size totransmit all the pressure required to make and maintain for all time a perfect electrical contact.

From the foregoing it will be seen that the principal feature of my invention is that the belectrical connection between the ends of the resistance-rodk and the metallic terminal is maintained perfect at all times during the life of the rheostat by causing the pressure required to make a perfect contact to be transmitted to the joint through the elasticity of a spring' or other elastic medium that is strong enough to transmit this pressure. So far as I know this feature has never been used in a rheostat of this kind.v .Therefore I claim it broadly.

I claim- 1. rlhe combination of a plurality of electrical resistance-rods made of carbon or a similar material, metallic terminals, clampingscrews for pressing said terminals -iirmly against the ends of the rods and a single spring common to a plurality of rods, intervening between the screws and terminals, substantially as described."

2. The combination of a pluralityof electrical resistance-rods made of carbon or a similar material of low conductivity, metallic terminals, clamping-screws, pressing the terminals against the ends of the rods, a single spring common to a plurality of rods and through which the pressure of the clampingscrews is transmitted, and a protective casing made of insulating material that is fireproof, for the rods.

3. The combination of a plurality of electrical resistance-rods such as described, rnetallic terminals, a single spring common to a plurality of rods, clamping-screws acting to compress the springs against said terminals, to

press the terminals against the rods substantially in the manner described, and a casing of non-conducting materialcovered with iron protecting the rods and the terminals.

ff. The combination of a plurality of electrical resistance-rods made of carbon or similar material, metallic terminals, a single spring common to a plurality of rods, clamping-screws acting through the intervening springs and pressing the terminals against the ends of the rods, a covering of tireproof insulating material for the rods, and a metallic casing protecting externally the insulating material.

5. The combination of a plurality of electrical resistance-rods made of carbon or a similar material of low conductivity, metallic terminals, clamping-screws for forcing the terminals against the ends of the rods, a single spring common to a plurality of rods compressed against the terminals by the screws substantially in the manner described, a tube made of glass, porcelain, mica, asbestos, or a similar material in which the rods and the terminals are placed, and a metallic covering for protecting the tube.

6. The combination of an electrical resistrial, a tube of fireproof insulating material in which the rod is placed, a metallic covering for protecting the tube, metallic termi'- nals for the rod, springs pressing the terminals against 'the rods, clamping-heads bearing against the springs and screws engaging' the clamping-heads for compressing the springs.

7. The combination of an electrical resistance-rod made of carbon or a similar material, a protective casing for the rods made of glass, porcelain, mica, or similar insulator, metallic terminals, springs holding the terminals against the ends ofthe rods, clamping-heads bearing against the springs and screws engaging the clamping-heads for compressing the springs. Y y

8. The combination of an electrical resistance-rod made of carbon or a similar mate rial, a tube of lireproof insulating material for protecting the rod, metallic terminals, springs pressing the Aterminals againstrthe rods, clamping-heads bearing againstthe springs and screwsengaging the clampingheads for compressing thev springs.

9. The combination of an electrical resistance-rod made substantially as described, an iron-clad casing made of insulating' material in which the rod is placed, metallic ends, springs holding the ends against the rods, clamping-heads bearing against the springs, and screws engaging the clamping-heads for compressing the springs.

lO. Thecombination of an electrical resistance-rod made of carbon, metallic oXid or a similar material, a casing of non-conducting material for the rod, metallic terminals, springsholding the terminals against the rod,

`ance-rod made of carbon or a similar mate- IOO rio

clamping-heads bearing against the springs,

and screws engaging the clamping-heads for compressing the springs.

11. The combination of an electrical resistance-rod such as described, a tube of glass, porcelain, mica, asbestos, or a similar material for the rod, a metallic covering for the tube, metallic terminals, springs pressing the terminals against the rods, clamping-heads bearing against the springs, and screws engaging the clamping-heads for compressing the springs.

12. In a rheostat, the combination of the rods 5, the casings 6, the pipes 1, the terminals 7, the connectors 8, springs acting to force ,the terminals against the rods, the insulation 9 made of yielding material, the clampingheads 2 and 3, and screws or bolts arranged to draw these heads in a direction to compress the springs.

13. The combination of resistance -rods made substantially as described, metallic terminals at the ends of the rods, connectors for connecting these terminals with each other or with circuit-wires, the springs 10, the insulation 9, the clamping-heads 2 and 3, and screws arranged to draw the heads together and compress the springs.

14. The combination of resistance rods made of carbon or a similar material oi' low conductivity, a protective casing for the rods, the metallic terminal plugs 7, the connectors 8, the springs 10, the insulation 9, the clamping-heads 2 and 3, and the screws arranged to draw the heads together and compress the springs.

15. The combination of resistance rods made of carbon or a similar material, a tube of insulating material, incasing said rods, a metallic cover protecting the insulating-tubes, metallic terminals arranged to bear against the ends of the rods, connectors to connect the terminals with each other and with a circuit, compressed springs acting to force the terminals against the rods, a layer of insulating material separating the springs from the terminals and connectors, clamping-heads arranged to compress the springs and screws to tighten the clamping-heads.

16. The combination of the rods 5, casings 6, pipes 1, terminals 7, connectors 8, springs 10, retaining-pii'is 11, foot-plates 12 a layer of insulation separating foot-plates from terminals 7 and connectors 8, clamping-heads to compress the springs, and screws to draw the heads together.

17. The combination of resistancerods made substantially as described, metallic terminal plugs 7, the connectors 8, springs 10, pins 11, plates 12, and a layer of insulation between the plate 12 and the connectors 8. clamping-heads constructed with recesses to receive the springs, and screws arranged to tighten the clamping-heads.

18. The combination of resistancerods made of carbon or a similar material, a protecting-casing in which said rods are placed, metallic terminals arranged to bear against the ends of the rods, connectors for connecting the terminals with each other and with a circuit, compressed springs to force the terminals against the rods, the insulation 9 made oi' a yielding fireproof material, clamping-heads made with recesses to receive the springs, and screws to tighten the clamping-heads.

19. The combination of resistance rods made of carbon or a similar material, ot' low conductivity, a tube of insulating material incasing the rods, a metallic cover for protecting the insulating-tube, the metallic terminal plugs 7, the connectors 8 constructed with a side extension to connect with circuit-wires, compressed springs to force the terminals against the rods, the insulation 9 made oi' a yielding tireproof material such as asbestos, clamping-heads provided with recesses to accommodate the springs, and screws to draw the heads together.

20. The combination of resistance rods made of carbon or a similar material, casings of iireproof insulation for the rods, a metallic covering for the insulation, metallic terminals placed at the ends ot' each rod, connectors to connect the terminals with each other and with circuit-wires, the springs 10 and footplates 12, the insulation 9, clamping-heads to compress the springs and screws arranged to draw the heads together.

21. The combinationof resistance-rods such as described, metallic terminals to bear against the rods, connectors to connect the terminals with each other and with circuit-wires, springs acting to force the terminals against the ends of the rods, a layer of insulating material separating' the springs from the connectors, the clamping-heads 2 and 3 and the clampingbolts 4 4.

22. The combination of resistance rods made of carbon or a similar material of low conductivity, a protective casing for the rods, the metallic terminals 7, the connectors 8 having side extensions to connect with circuitwires, compressed springs to force the terminals against the rods, a layer of insulation to separate the springs from the connectors, the clamping-heads 2 and 3, and the tighteningbolts 4.

28. The combination of resistance rods made of carbon or a similar material, casings of fireprooil insulating material for the rods, a metallic covering for the insulating material, metallic terminals 7, connectors 8, springs 10, plates 12, an insulating layer between 12 and 8, clamping-heads 2 and 3, and tighteningbolts 4.

24. The combination of resistance-rods made of carbon or a similar material, metallic terminals placed at the ends of the rods, connectors to connect the terminals with each other and with circuit-wires, the insulation 9 made of a yielding iireprooil material, the

IOO

springs 10, and foot-plates 12, the heads 2 and 3, and bolts 4.

25. The combination of resistance rods made of carbon or a similar material, a tube of insulating material for the rods, a metallic tube Jfor the insulating material, the metallic terminal plugs 7, the connectors 3, the springs 10, pins 11, and plates 12, the insulation 9 made of a iireprootl material, the heads 2 3 and tightening-bolts t.

26. The combination of resistance rods made of carbon or asimilar material, casings of fii'eproo'f insulating material for the rods, a metallic cover for the insulating material, metallic terminals arranged to bear against the ends of the rods, connectors for connecting the terminals with each other or with circuit-wires, springs to force the terminals against the rods, the insulating layer 9, the clamping-heads 2 3, and screws or bolts arranged to draw the heads together.

27. The combination or' resistance rods made of carbon or a similar material, tubes of insulating material incasing the rods, metallic covers for the insulating-tubes, the metallic terminal plugs 7, the connectors 8 having side extensions for connecting with circuitwires, the springs 10, pins 11, and plates 12, a layer of insulating material separating the connectors from 12, the clamping-heads 2 and 3, and tightening screws or bolts Jfor drawing the heads together.

28. The combination of resistance rods made of carbon or a similar material, a protective casing for the rods, metallic terminals placed at the ends of the rods, connectors to connect the terminals with each other and with circuit-wires, the springs 10, a layer of insulation separating the springs from the connectors, the clamping-heads 2 and 3, and the bolts 4.

29. The combination of the resistance-rods 5, casings 6, protecting-pipes 1, terminals 7, connectors 8, compressed springs to force the terminals against the rods 5, a layer o1 insulation to separate the springs from the connectors, the heads 2 and 3, and bolts or screws to draw the heads together.

30. The combination of resistance rods made of carbon or a similar material of low conductivity, a casing of lireproof insulating material for the rods, a metallic covering for the insulating material, the metallic terminal plugs 7, the connectors 8 having side eXtensions to connect with circuit-wires, the springs 10, pins 11, and plates 12, separated from the connectors by the insulation 9, clamping-heads having recesses to receive the springs and screws arranged to move the heads in a direction that will compress the springs.

31. The combination of resistance rods made of carbon or a similar material, a protecting-casing for the rods, metallic terminals 7, connectors to connect the terminals with each other orwith circuit-wires, springs 10,

the insulation 9 made of a yielding lireproof material, clamping-heads arranged to compress the springs, and screws to tighten the clamping-heads- 32. The combination oi' resistance-rods such as described, metallic terminals arranged to bear against the ends of the rods, connectors to connect the terminals with each other and with circuit-wires, the springs 10 pins 11 and plates' 12, separated from 8 by the insulation 9, clamping-heads arranged to compress the y springs, and screws to tighten the clampingheads.

33. The combination of resistance-rods made of carbon or a similar material, insulating-casings for the rods, made of tireproof material, a metallic covering protecting the insulating-casings, metallic terminals placed at the ends ot' each rod connectors to connect the terminals having side projections to connect with circuit-wires, compressed springs to force the terminals against the rods, the insulation 9 clamping-heads adapted to compress the springs, and screws arranged to move the heads in the direction that will compress the Springs.

34.' The combination of resistancerods made ot' carbon or a similar material, a tube of insulating material for the rods, a metallic cover for the insulating material, the metallic terminal plugs 7, connectors for connecting the terminals with each other and with circuit-wires, compressed springsto force the plugs against the rods, the insulation 9, clamping-heads to compress the springs, and screws arranged to tighten the heads.

35. -The combination of resistance rods made of carbon or a similar material, protective casings for the rods, metallic terminals arranged to bear against the ends of the rods, connectors for connecting' the terminals togetherV and with circuit-wires, compressed springs to hold the terminals against the rods, the insulation 9, clamping-heads having recesses to accommodate the springs, and screws IOO adapted to move the heads in a direction that ing-heads adapted 'to compress the springs,

and screws arranged to tighten the clamping'- heads. Y

37. The combination of resistance rods made of carbon 0r a similar material, a protecting-casing for the rods, the metallic terminal plugs 7 ,the connectors 8 having extensions Afor connecting with circuit-wires, compressed springs to force the terminals against the rods,

IIS

a layer ol insulatingl material separating the springs from the connectors and the terminals, clamping-heads having recesses adapted to receive the springs, and bolts arranged to draw the heads together.

38. The combination with a resistancer0d formed ot' material of low eonductivityin one part oi' the body, and of a material oi higher conductivity in another part of its body, of terminals contacting with the material ot' higher conductivity.

rods and means for adjusting' the tension ot" said spring.

al. In a rheostat, the combination of a plurality ot' resistance-rods, heads between which said rods are held, a iixed frame in which said heads are movably sumuorted, and a spring interposed between the frame and one ot' the heads and serving to firmly press said head against the ends of the rods.

42. Ina rheostat the combination with a pluralityot' resistance-rods of carbon or the like, of a plurality of connectors contacting with the ends oi' the rods, and elastic means maintaining such contact at one end.

43. In a rheostat, a plurality of resistancerods oi' carbon or the like, metallic terminals or heads between which the rods are held, and an elastic medium bearing against one o't' the terminals or heads for pressing the same lirmly against the rods.

The foregoing specilication signed this 4th day of March, 1903.

VILLIAM BAXTER, J n.

In presence of- STEPHNN H. OLIN, JOHN PHAIP.. 

